Mutations of ras genes are found in about 30% of human tumors. The gene group consists of three kinds of families, including K-ras, N-ras, and H-ras, in which K-ras mutations are most frequently found in lung adenocarcinoma cells. Mice bearing such mutations demonstrate the most common histopathologic subtype of non-small cell lung cancer with short latency and high penetrance. Phosphatase and tensin homolog deleted on chromosome 10 hereinafter, referred to as “PTEN”), which catalyzes phosphorylation at the 3-position of the inositol ring phosphatidylinositol-3,4,5-triphosphate, is known as a tumor suppressor gene that suppresses the Akt signaling pathway to regulate the growth and survival of cells.
The fact has been known that Akt is activated in cancer cells by either activating the growth factor receptors of Ras or inactivating PTEN.
It was shown in recent reports that about 90% of non-small cell lung cancers are involved in the continuous activation of the PI3K/Akt pathway, and this activation of Akt promotes cellular survival and resistance to chemical therapy or γ-ray irradiation.
In addition, K-ras mutations can increase the activity of lung adenocarcinoma cells by the activation of Akt.
In view of such facts, a method of regulating the Akt is needed for the treatment of lung cancer.
Meanwhile, a method for the noninvasive delivery of genes by inhalation is known for the treatment of lung cancer.
Recombinant viral vectors have been used as effective gene delivery carriers because they have high affinity for airway epithelium and can be efficiently transfected into lung cells.
However, recombinant viral vectors, such as recombinant adenoviral vectors, have had limitations in their actual application because they have toxicity, cause immune response by repeated administration and are difficult to mass-produce.
Non-viral vectors have advantages in that they are easier to use than the viral vectors and cause less immune response. Furthermore, they also have the ability to be able to deliver high-molecular-weight DNA molecules.
Several recent studies have demonstrated that the binding of DNA with cationic polypeptides, such as polylysine, polyethylenimine (PEI), protamine, and histone, may be useful for gene delivery both in vivo and in vitro.
Among such polypeptides, PEI has received attention as a carrier for gene delivery because of its stability in an aerosol form. However, the use of PEI has been limited because of its strong toxicity caused by the characteristic accumulation of polycations.
Many researchers have studied possibilities for the direct delivery of various therapeutic agents into the lungs and the pulmonary lymph nodes by nebulization, and at the same time, attempted to use PEI as a gene therapy carrier, however, PEI has been reported to induce potential toxicity by accumulation.
Accordingly, in order to use polypeptides as gene delivery carriers, the following processes are necessarily required: adhesion to the cell surface endocytosis, isolation from endosomal lysosomal networks, migration into the cell nuclei, vector unpacking, and the like.
Therefore, there is a need for the development of an efficient and stable carrier for the aerosol delivery of a gene, which meets such requirements.